from the syrian regimes, denials, which the obama white house which for a year has called the chemical weapons use in syria a red line is now being cautious as it calls for an investigation. you're about to see what the rebels say is the evidence, some of it very graphic. our chief foreign correspondent richard engel joins us now with that. richard? >> reporter: good evening, lester. more videos emerge from syria today. they are unconfirmed by nbc news, but they are consistent with the accounts of witnesses we spoke to. and, again, these images are graphic. the syrian government bombed villages outside damascus today, the same villages hit yesterday by what looks like a war crime. an outrage. hundreds killed by chemical weapons, the rebels say, many of them buried today in mass graves. a syrian cameraman contracted by our partner itn filmed people looking at an exploded rocket. near it, dead bodies. nbc news has no way to confirm that the casualties were caused by this weapon. there is still no definitive proof that chemical weapons were used or by whom. but how can anyone fake rows of